Studies in this laboratory focus upon an analysis of the neural control of cardiac dynamics and rhythm in behaviorally conditioned, unanesthetized animals. Previous studies have indicated that post-myocardial infarction cardiac arrhythmias occur principally within a specified range of heart rates (the "critical HR range" hypothesis). Rhesus monkeys will be operantly conditioned to control their heart rates at levels which are below, within, and above the probable critical range. They will then be subject to experimental coronary occlusion and tested in the operant conditioning paradigm to assess the validity of the "critical HR range" hypothesis. In addition, baboons will be operantly conditioned to elevate their arterial blood pressure by 30 mm Hg for minute long intervals. The behavior of individual segments of myocardium will be assessed using ultra-sonic "segment-length" gauges during periods of rest and blood pressure elevation both before and after coronary arterial occlusion. Finally, the cardiovascular responses of chronically instrumented dogs to acute coronary arterial occlusion. Finally, the cardiovascular responses of chronically instrumented dogs to acute coronary occlusion will be examined in normal animals and animals subject to surgical cardiac denervation. Each of the above projects is designed to elucidate a specific facet of the neural control of the normal and ischemic heart of intact, non-anesthetized animals.